Nowadays, organic light-emitting diode (OLED) display devices are widely used in the display field. OLED display devices may provide excellent characteristics including a low power consumption level, a high color saturation level, a wide viewing angle, and a thin dimension. The OLED display devices may be used as flexible display.
Generally, an OLED display device includes a base substrate. The OLED display device also includes an anode layer, a hole injection layer, a hole transport layer, a light emitting layer, an electron transport layer, an electron injection layer and a cathode layer, which are laminated sequentially on the base substrate. When a voltage is applied between the anode layer and the cathode layer, a current is formed there-between. The electrons in the cathode layer are transported through the electron injection layer and the electron transport layer. And the holes in the anode layer are transported through the hole injection layer and the hole transport layer. When the electrons and the holes are combined at the light emitting layer to form electron-hole pairs, the light emitting substances are excited in the light emitting layer to emit light.
Among all the materials, ITO (Indium Tin Oxide) has stable chemical properties and high conductivity and has been widely used in the anode layer of the OLED display device. However, the ITO material has low work function of about 4.5 eV-4.8 eV. Although the work function of the ITO material may be increased by physical treatments of oxygen plasma, ultraviolet (UV) radiation under ozone environment, etc., it is difficult to increase the work function of the ITO to reach 5.0 eV, which is still below the HOMO (Highest Occupied Molecular Orbital) of most of the hole injection layers and hole transport layers. Due to the low work function of the ITO material, the hole injection and hole transport capability are significantly reduced. This adversely affects the light emitting performance of the OLED display device.
Therefore, it is desirable to lower the hole injection barrier and to enhance the injection and transport capability of the holes in an OLED display device. The present disclosure is directed to solve one or more problems set forth above.